There isn’t much talking in the movie “Styx,” which is set almost entirely on a sailboat in the middle of the Atlantic Ocean. For the first half of this spellbinding — and unexpectedly gut-wrenching — little film, there’s barely any dialogue at all, apart from the occasional radio exchange between the boat’s hyper-capable captain (Susanne Wolff) and a disembodied voice, warning her, from an unseen vessel, of an approaching storm. Like 2013’s “All Is Lost,” there’s an inherent fascination in witnessing an individual cope with the elements, against the vastness of the high seas.

But all that changes when the woman, Rike, comes out on the other side of the storm to discover a disabled and slowly sinking ship filled with more than 100 African refugees, some of whom have begun jumping overboard — only to drown — in their desperation at the prospect of rescue. When Rike contacts the coast guard with a mayday call, she is warned to back away; her presence gives false hope, she is told, and her tiny boat cannot accommodate that many people. But one straggler clinging to a life preserver, a 14-year-old boy named Kingsley (Gedion Oduor Wekesa), manages to make it to the side of Rike’s boat, where he is taken in, shivering, dehydrated and badly injured.

From that moment on, “Styx” becomes a kind of moral allegory, crossed with an almost unbearably tense nautical thriller. Rike wants to help the others (including Kingsley’s sister, back on the ship), but she also recognizes the limitations of one person’s ability to do so. While she reluctantly waits for help, she’s reduced to an impotent witness.

Susanne Wolff plays the captain of a small sailboat en route from Gibraltar to Ascension Island in “Styx.” (Benedict Neuenfels/Beta Cinema)

This may be how many people watching feel about Rike’s situation, albeit less acutely and with none of the immediacy. As Austrian director Wolfgang Fischer and his co-writer Ika Künzel suggest, those of us who watch passively — or worse, choose to look away — while a seemingly unending flood of refugees struggle to reach our shores may also be the ones in need of saving.

“Styx” is, paradoxically, a beautiful, if eccentric film. Opening in Gibraltar, where Rike practices emergency medicine, the film focuses, at times, away from the dramatic to the mundane: a Barbary macaque, a traffic accident and, later, on Rike’s boat, on a piece of crumpled food wrapper slowly expanding, like a flower. Everything feels at once ordinary and otherworldly, evoking a sense of the surreal in the everyday.

Wolff is never less than mesmerizing in this role, which demands a performance that is, at times, more physical than emotive. She’s like a dancer: straining and exerting in a ballet of movements that convey meaning not by words, but actions. And when her character is, by the end of the film, reduced to something like catatonia, her drained silence speaks volumes, echoing the way the audience, at that point, probably also feels.

Unrated. At the Avalon. Contains mature thematic elements, brief strong language and some disturbing images. In English and German with subtitles. 94 minutes.

Michael O'SullivanMichael O'Sullivan has covered the arts for The Washington Post since 1993, contributing reviews and features on film, fine art, theater and other forms of entertainment to Style and Weekend. Follow